The present invention relates to the casting of molten metal from ladles into ingot molds, and has to do more particularly with means for measuring the molten metal level in ladles and for detecting the approach of slag toward the nozzle of the ladle so that slag contamination of the ingots being poured can be effectively eliminated.
It has hitherto been proposed to detect the slag-metal interface by means of a pair of electrodes or probes mounted in the ladle wall one above the other in close proximity to the teeming nozzle. When both probes are in contact with molten metal, virtually no potential is present across the probes; but as the metal level recedes, a level is reached when the upper probe is in contact with the slag and the lower probe is still in contact with the molten metal. This results in a potential across the probes which is used to operate a signal instrument which is hung on the ladle during teeming. The probes are positioned so that the signal will occur when a predetermined metal level has been reached in the ladle, whereupon, when the alarm sounds, the quantity of metal remaining in the ladle can be calculated and a determination made if and when a trailer ingot should be poured to avoid an unrollable butt.
Numerous difficulties have been encountered with systems of the character described. In particular, the systems are unreliable and give a faulty indication of metal depth if the ladle is tilted. Numerous operational and maintenance problems were encountered due to the handling of the electronic package which had to be hung on each ladle during the teeming operation, as well as the hostile environment encountered by the electronic package when hung on the ladles. In addition, the electronic packages were battery operated and subject to rapid battery deterioration and failure. The probes themselves are subject to rapid deterioration and must be replaced frequently. Heretofore, the probes were inserted through holes drilled through the ladle shell, tank, and the working lining, the outwardly projecting ends of the rods being connected to the electronic package by alligator clips. With such arrangement, it is difficult to make reliable electrical connections between the probes and the electronic package.
In contrast to the foregoing, the present invention provides an improved slag level detecting system which effectively eliminates the numerous difficulties encountered with the systems formerly in use, and provides a system which is accurate, as well as easy to maintain and service.